A fluorescent protein, for example, a green fluorescent protein having an amino acid sequence represented by SEQ ID NO: 6 of a sequence listing is generally used as a material for fluorescently labeling a protein in basic research and application research. Fluorescent labeling with a fluorescent protein enables the observation of localization and movement of a protein under an optical microscope. Further, a fluorescent protein that responds to environment, such as cytoplasmic pH and calcium concentration, has also been created by genetic engineering modification (Patent Documents 1 and 2). The fluorescent protein capable of responding to a cytoplasmic environment change is a very potential tool for checking life phenomenon.
On the other hand, conventionally, it has been suggested that there is a strong correlation between the pressure in a living body and the life phenomenon, as is found in the fact that the shape of a tissue which is being generated is determined by a pressure in a cytoplasm.